To perform fitting operations, the beads of a tire must first of all be bead broken from the edges of the rims on which they are normally fitted during wheel use.
To perform this operation, two technical solutions are provided in the prior art.
According to a first technical solution, tire-changing machines have an arm on the side of the base frame that has one end joined to the base frame, so as to turn on a plane parallel to the ground, and that has an opposite end with a bead breaking blade.
To bead break the beads, an operator turns the arm outward, so as to move it away from the side of the base frame, and then positions a wheel with the tire previously deflated, against the side in a substantially vertical position and, finally, starts a linear actuator located between the base frame and the arm, so the arm is recalled toward the side and, at the same time, the bead breaker blade presses on a bead segment of the tire, detaching this from the edge of the rim.
This operation is repeated several times, every time turning the wheel so the blade operates on the entire circumference of a bead turned outward and then, after turning the wheel on itself, is also repeated for the other bead.
When the tire is completely bead broken, it is substantially loose on the rim and the operator grips it and places it, together with the rim, on the swivel platform; on the latter the rim is secured by means of special grip parts and the operator proceeds to remove the tire from the rim.
For this operation, the operator uses a tool fitted on the fixed turret with the interposition of an adjustable support arm, which is shaped so as to be able to be wedged between the rim and the tire so that when the swivel platform is turned, the tool causes the bead to gradually exit from the edge of the rim with the consequent removal of a first side of the bead.
It must be pointed out that to wedge the tool between the tire and the edge of the rim, the operator must also use a lever with which he manually lifts a first portion of the tire off the rim, in such a way as to obtain a passage wide enough to insert the tool.
According to another technical solution, used to bead break the tires of particularly delicate wheels, such as, for example, the wheels of sports cars with light-alloy rims, the tire-changing machines have one or two bead-breaking tools that operate on the beads of the tires when the wheel is already positioned and fixed on the swivel platform.
Each tool consists of a disc shaped like a truncated cone and supported free to turn at the end of a corresponding support arm mounted on the tire-changing machine alongside the fixed turret.
Each disc has the edge of larger diameter intended to be placed in contact with the tire bead, at a point very close to the edge of the rim.
Each arm has its own operating system that raises or lowers it and which, therefore, determines the pressure of the disc on the bead turned upwards or the lifting from below upwards of the bead turned toward the ground; the operating system also normally envisages turning the arm, or each arm, when there are two, between a work position turned toward the swivel platform and a rest position away from this, and vice versa.
When there are two discs, one is mounted on an arm so it can press in a direction from the top downward on the upper bead while the other is mounted on another arm so it can press on the bead turned toward the ground in a direction from below upward.
The pressing action is normally done in a coordinated and contemporaneous way and the tire is completely beaded by rotating the platform while both discs press on the respective beads, turning freely on these.
Subsequently, to remove the tire from the rim, the operator proceeds as previously described both using the lever and completing removal by means of the tool fitted on the arm of the column of the tire-changing machine.
This state of the art has a number of drawbacks.
A first drawback is that to support the beading tools, the tire-changing machines must have special arms alongside the fixed turret on which, as it has been said, are fitted the tools for removing and fitting the tires on the rims.
Another drawback is that the arms must be positioned independently the one from the other and in such a way that the edge that has to be placed in contact with the bead is neither too close to the edge of the rim nor too far from this.
In the first case, the rims could be damaged during bead breaking operations, while in the second case, damage could be caused to the side of the tire, i.e. the side area of the tire between the beads and the tread, which is considerably more flexible and fragile than the beads.
A further drawback is that the correct positioning of the lower arm and, therefore, of the relevant disc on the corresponding lower bead, is very difficult because visibility is strongly reduced by the tire itself, by the rim, by the platform and by the base frame of the tire-changing machine.
Furthermore, the free space between the platform and the base frame is strongly limited and for this reason it is even more difficult for the operator to visually control, in a direct way, the correct positioning of the lower bead breaking disc.
Some manufacturers of tire-changing machines, to try and at least partially solve this problem, have equipped the tire-changing machines with a reflection member, typically a mirror, fitted near the lower face of the swivel platform, which allows the operator to observe the image reflected from below upwards of the tire area on which the bead breaking disc has to rest.
Other manufacturers have decided to fit a camera instead of the mirror and have also equipped the tire-changing machine with a small screen connected to the camera that allows the operator to observe the bead area during the positioning of the lower bead-breaking disc.
These solutions have further drawbacks.
Another drawback is that the costs of the reflecting devices or of the cameras and of the screens connected to these negatively affect the total costs of the tire-changing machines.
Another drawback is that the field of vision of the reflecting devices or of the cameras is considerably limited and in any case produces an indirect vision which is therefore subject to optical distortions.
Another drawback is that the operating space in the area between the lower face of the platform, in itself already very small, is further reduced by the presence of these devices.
A further drawback is that both the reflecting devices and the cameras are subject to becoming quickly dirty and, therefore, to be able to help the operator in his/her work, they require frequent cleaning and maintenance.
A further drawback of the known tire-changing machines is that the arms that support the bead-breaking tools are fitted on the base frame of the tire-changing machines separately from the fixed turret and each of these has to be driven by its own actuator.
This results in a considerable increase in the overall dimensions of the tire-changing machines and in their having a fairly complicated structure both in terms of manufacture and function.